My kids both have basic 20" wheeled bicycles. Single speed with front and rear brakes. Ive been taking them to some very light off road trails w/ a few 2-3 inch drops and bumps. I believe the steer tubes are threaded 1".

My questions is: Are their any suspension forks made for 20" bikes? Is it possible to change out the forks from ridge to suspension?

The bikes they have are just fine and very durable. I dont see why I should buy a brand new bike, when I could just change out the fork as an upgrade. Anyone help me out with this? thanks!

Most kids suspension bikes are piles of cat poo, whether full or front only.

It's better that they develop their skills on a rigid bike, because they do it at a speed they are capable of handling. If they have cheap suspension it's like riding a pogo stick - no damping. But, it encourages them to go faster than their skill level allows, so they then crash harder.

2-3inch drops and a few bumps should be within their capabilities - if not, then they should practice until they can deal with them. Some of our youngest kids have just done the regional school mtb champs and even the newbies coped with similar surfaces.

If they're nervous at 2-3 inch "drops", get them to go over them a few times until they're confident at doing it, then gradually increase the difficulty. Usual rules apply: stand up, keep knees and arms bent, weight back and let bike ride underneath them while their bodies/heads stay level.

Set up some artificial obstacles in a safe area (plank on brick, plank on two bricks, plank onto pallet and ride off - or even ride off kerb

There's also the fact that a bike designed with rigid forks may not be suitably proportioned if you install a suspension fork.

Once they can handle these and more severe obstacles and they're big enough for a better bike, they'll have the skill levels to handle the greater speeds that suspension allows.

Most kids suspension bikes are piles of cat poo, whether full or front only.

It's better that they develop their skills on a rigid bike, because they do it at a speed they are capable of handling. If they have cheap suspension it's like riding a pogo stick - no damping. But, it encourages them to go faster than their skill level allows, so they then crash harder.

2-3inch drops and a few bumps should be within their capabilities - if not, then they should practice until they can deal with them. Some of our youngest kids have just done the regional school mtb champs and even the newbies coped with similar surfaces.

If they're nervous at 2-3 inch "drops", get them to go over them a few times until they're confident at doing it, then gradually increase the difficulty. Usual rules apply: stand up, keep knees and arms bent, weight back and let bike ride underneath them while their bodies/heads stay level.

Set up some artificial obstacles in a safe area (plank on brick, plank on two bricks, plank onto pallet and ride off - or even ride off kerb

There's also the fact that a bike designed with rigid forks may not be suitably proportioned if you install a suspension fork.

Once they can handle these and more severe obstacles and they're big enough for a better bike, they'll have the skill levels to handle the greater speeds that suspension allows.

I'm w/atbman. I still have my original (mid-'80s) rigid Mongoose mountain bike, and even though I've owned half a dozen since then, I still enjoy taking it out and thrashing over the trails on which I developed my skills, such as they are. It's a great way to learn.
One thing that may help is to use the largest possible tires on the front, at the lowest pressure you can without pinch flats (for kids, you should be able to go into the low 30psi range, or even the 20s). When my Mongoose was new, I weighed 220 pounds, and I ran 2.1-2.3 tires at 40psi with few problems, even in the rocks.

As long as the kids' bikes aren't of the cheap department store variety- and it sounds like they aren't- the bikes should be able to handle skill building activities like those that atbman describes. My young cousin, all of 90 lbs. at the time, collapsed the front fork on such a bike doing routine curb jumping.